A new book describes how dogs around the world have evolved traits that are suited to the environments and human cultures they live alongside; fMRI research completes the picture, showing that dog brains distinguish between human expressions of fear, anger and sadness and respond uniquely to smiles
A sturdy sled dog in the Arctic, a small, agile hunting dog in a tropical forest, and a pet dog lying awake in a brain scanner seem to come from different worlds. But they all represent different stages and paths in the millennia-long relationship between dogs and humans.
A new book by archaeologist Professor Peter Mitchell of the University of Oxford describes how dogs evolved alongside different human societies and acquired traits that suited the environments, food sources and roles that humans assigned to them. A separate study, published in the journal iScience, adds the brain dimension to the picture: pet dogs are able to distinguish not only between happy and negative faces, but also between human expressions of fear, anger and sadness.
There is no direct connection between the two publications. The book is based on a synthesis of archaeological, genetic, and ethnographic findings, while the study is a small fMRI experiment in pet dogs. Together, they raise a broader possibility: that life alongside humans has changed not only the dog's appearance, size, and roles, but also the way it perceives and processes human social information.
Domestication that did not happen in one moment
In his book First Dogs: Hunter-Gatherers and Their Canine Companions from Prehistory to the Present, Mitchell argues that the domestication of dogs was not a one-time event in which humans captured wolves and quickly domesticated them. He argues that it was a long, multi-stage process in which both humans and the wolf ancestors of dogs took an active part—at least in the early stages.
Archaeological findings show that dogs were buried alongside humans as early as 14 years ago. They appear in ancient art from all continents and occupy a place in the mythologies, religions, and traditions of many societies. Throughout history, they have assisted in hunting, guarded camps and homes, herded livestock, pulled sleds, and carried loads, but they have also served as companions.
Mitchell particularly emphasizes the importance of hunter-gatherer societies. The relationship with dogs began long before humans domesticated most farm animals and crops. At this point, dogs were not just property or tools, but companions who helped locate prey, chase, protect, and warn of danger.
According to the picture presented in the book, there was no single way to transform a wolf into a dog. Different groups of dogs evolved along different paths depending on human societies and the environments they lived in. Humans favored dogs that were endowed with useful traits, but dogs themselves also adapted to the opportunities offered by human camps: available food, protection, and cooperation in hunting.
Dogs adapted to cold, altitude, and rainforests
One of the most prominent examples comes from the Arctic region, where indigenous communities developed cultures based on sled dogs. The northern dogs had thick fur, a sturdy build, and limbs capable of withstanding the prolonged strain of dragging loads through the snow.
Examination of ancient dog skeletons has revealed characteristics associated with this work, including strong limb bones and signs of stress in the vertebrae. Isotope analysis of the bones has shown that in some coastal areas dogs and humans shared a similar diet, based largely on marine food sources. Dogs not only lived in the community's environment, but were integrated into its subsistence system.
At the Tibetan plateau, humans and dogs faced a different problem: oxygen-poor air. Genetic studies have found that local dogs have adaptations that help them live at high altitudes, paralleling adaptations that evolved in human populations in the region. Mitchell notes that it is not yet certain when dogs arrived at the plateau and how they acquired the changes, but without such adaptations, the high altitude could have limited their spread.
Dogs that lived with hunter-gatherers in the tropical forests of South America and Southeast Asia developed different characteristics. Instead of having a heavy body suitable for pulling sleds, they tended to be small, agile, and able to move through dense vegetation and track prey in complex terrain.
Ethnographic evidence suggests that indigenous communities carefully selected puppies that showed desirable hunting skills and managed breeding to preserve the traits. In some places, the dogs may even have been crossed with local wild dogs to add new traits, although the full history of these crossbreedings is difficult to reconstruct today.
Dogs that also provided raw material
Not all dogs were bred for hunting, guarding, or transportation. On the northwest coast of North America, some indigenous communities bred small, hairy dogs whose fur was used to make cloth and ceremonial blankets. This is an extraordinary example of selection for a role that resembles a domesticated animal that provides fiber.
In other regions, dogs were selected for physical or behavioral characteristics that were considered to have spiritual and ceremonial significance. The variety of dog forms around the world thus reflects not only adaptations to temperature or terrain, but also the values, traditions, and needs of human societies.
Diseases also influenced their distribution. In sub-Saharan Africa, for example, diseases such as trypanosomiasis and ehrlichiosis may have made it difficult for dogs originating from temperate and northern regions to establish themselves. This may explain why dogs arrived relatively late in some tropical regions or remained rarer there.
A genetic heritage that disappeared with colonialism
Genetic studies show that many of the ancient dog populations no longer exist in their original form. European dogs that spread around the world during the colonial period replaced or interbred with local populations, blurring genetic signatures that had been formed over thousands of years.
Therefore, it is not always possible to infer from the distribution of modern dog breeds what the populations that lived alongside hunter-gatherers or ancient societies looked like. In some areas, genetic remnants of local lineages remain, but in others, their stories can only be reconstructed through skeletons, ancient art, and historical descriptions.
Mitchell concludes that the transition from wolf to dog was not a single event. It is a long process that continues, in a sense, even today. In recent times, and especially in the West, humans have gained greater control over the size, appearance, and behavior of dogs through deliberate breeding. Nevertheless, the relationship remains a product of dependence and cooperation between the two species.
From evolutionary history to the dog brain
A separate study, led by Raul Hernandez-Perez and Laura Cuya of the University of Vienna, examined another possible outcome of living alongside humans: the ability of dogs to read our faces.
In the first phase, eight dogs viewed pictures of strangers with happy or neutral faces. Happy faces triggered activity in the temporal cortex and caudate nucleus. The latter region is involved in reward and learning processes, so the researchers speculate that a human smile may have emotional or rewarding meaning for dogs.
In another step, 12 dogs were shown pictures of faces expressing happiness, anger, fear, and sadness. Machine learning analysis allowed the researchers to identify, based on the pattern of brain activity, which category of expression the dog saw.
The response to smiles was clearly different from the responses to negative expressions. However, whole-brain analysis showed that fear, anger and sadness were not processed in the same way either. This is the first finding to suggest that the dog's brain distinguishes between certain negative human facial expressions and not just between a positive signal and a threatening signal.
What the study does not prove
A brain scan cannot read a dog's mind. A different pattern of activity in response to a sad face and a scared face does not prove that the dog understands the person's inner experience or calls it "sadness" and "fear."
All of the study participants were family pet dogs. Free-ranging dogs, dogs raised with limited contact with humans, or wolves that have been socialized with humans may respond differently. The study also used static images, whereas in real life, dogs combine facial expressions with body movements, vocalizations, and scent.
Therefore, the fMRI study does not prove that the ability to distinguish between expressions arose as a result of domestication. It shows that the ability exists in the brains of the pet dogs tested. To prove its evolutionary origin, it would be necessary to compare different populations of dogs and wolves raised under controlled conditions.
Two layers of the same story
The book and the research are not part of a joint venture, but they complement each other. The book shows how dogs have changed their bodies, lifestyles, and roles to adapt to human environments and societies. Brain research points to a mechanism that allows them to adapt to our social world as well.
A dog that could recognize when a person was happy, angry, or scared might respond more appropriately, avoid confrontation, and cooperate in hunting, guarding, or working. This is a reasonable hypothesis, but the current study cannot yet show when the ability emerged or whether selection during domestication created it.
The broader conclusion is that the dog is not just a wolf that has changed its appearance. Thousands of years of companionship with humans have created a wide range of adaptations—from bones capable of carrying drag loads, to genes that help breathe at high altitudes, to a brain sensitive to subtle differences in human facial expressions.
More on the subject on the science website
- A wolf for a dog
- The common genetic basis for social behavior in dogs and humans has been discovered
- The evolution of puppy dog eyes
- Dogs have a dedicated area in their brain for voice recognition, just like humans.
- Adult wolves miss their handler when separated from them, just like dogs
Questions and Answers
When did dogs begin to live alongside humans? Joint burials of dogs and humans are known from about 14 years ago, but the process of rapprochement between humans and wolves probably began earlier and lasted a long time.
Did all dogs evolve the same way? No. Different populations were adapted to different roles and environments, including pulling sleds in the Arctic, hunting in tropical forests, living at high altitudes, and even providing fiber for weaving.
What did the brain scan study reveal? The brains of the dogs tested responded uniquely to happy faces and exhibited different patterns of activity in response to fear, anger, and sadness.
Does the study prove that domestication gave dogs the ability to understand us? No. The finding is consistent with this hypothesis, but proving it will require comparisons between pet dogs, free-ranging dogs, and wolves raised under similar conditions.
For the original publication: Opening the original publication
